Geomagnetically induced currents (GICs) in the power system cause half-cycle saturation of the transformers, malfunction of protective relays, reactive power loss, and voltage instability. A DC Flux Blocker (DFB) that can be installed in series with power system transformers tertiary windings to neutralize magneto motive force (mmf) due to GIC is described. The device consists of two circuit breakers, a low power and high current voltage source, which provides the magneto motive force of the GIC DC flux blocking function. The effectiveness of the proposed protective electrical device investigated and validated using the MATLAB software tool. The proposed method can effectively removes the flux due to GIC in both transformers and autotransformers that have tertiary windings. Since proposed method does not put any impedance in the neutral of the transformers so has no impact on protection schemes.
